Thursday, February 4, 2010

How much vitamin D? Vitamin D Council's recommendations




The Vitamin D Council has the following general recommendation regarding supplementation:
They also provide a specific example:






Ned Kock said...

I was just reading two posts by Hyperlipid (link below, two top posts) on vitamin D levels and cancer. To say that they were interesting is an understatement.

If I understand the posts correctly, the main message is that blood levels of vitamin D may be low or high, but they need to be kept at a constant level. Erratic supplementation leads to an increased risk of cancer, even if that leads to high levels of blood vitamin D on average.

Not as simple as one would think … life is not simple.

Ken said...

"Were ancestral Europeans deficient for vitamin D?

There are several problems with the vitamin-D hypothesis. First, if lack of this vitamin created the selection pressure that led to white European skin, why are Europeans genetically polymorphic in their ability to maintain blood levels of vitamin D? At least two alleles reduce the effectiveness of the vitamin-D binding protein, and their homozygotes account for 9% and 18% of French Canadians (Sinotte et al., 2009). If lack of this vitamin had been so chronic, natural selection would have surely weeded out these alleles. And why does European skin limit vitamin-D production after only 20 minutes of UV-B exposure? (Holick, 1995). Why is such a limiting mechanism necessary?" Why are Europeans white? .

Black-White Differences in Cancer Risk and the Vitamin D Hypothesis.

Ken said...

"Europeans are white-skinned because their ancestors had to maintain the same level of vitamin-D synthesis at latitudes where UVB radiation is much weaker. This leaves unexplained the much darker skin of indigenous peoples at similar latitudes in northern Asia and North America. More importantly, it posits vitamin-D metabolism as a ‘given’ that human skin color has to adjust to, when in fact this metabolic pathway is just as amenable to natural selection as everything else.[...]
For instance, many populations have long been established at latitudes where vitamin-D synthesis is impossible for most of the year. Some of these populations can get vitamin D from dietary sources (e.g., fatty fish) but most cannot. In these circumstances, natural selection seems to have adjusted their metabolism to reduce their vitamin-D requirements. We know that the Inuit have compensated for lower production of vitamin D by converting more of this vitamin to its most active form (Rejnmark et al., 2004). They also seem to absorb calcium more efficiently, perhaps because of a different vitamin-D receptor genotype (Sellers et al., 2003). Even outside the Arctic zone, there seem to be differences in vitamin-D metabolism from one population to another. In particular, vitamin-D levels seem to be generally lower in darker-skinned populations. [Here is confirmation of that even within populations the lighter skinned have lower vitamin D levels Pigmentation and Vitamin D Metabolism in Caucasians: Low Vitamin D Serum Levels in Fair Skin Types in the UK.]

Population differences in vitamin D metabolism (scroll down a bit)

Ned Kock said...


There is a tremendous among of genetic variation among Europeans today. This applies to almost any modern human group. Genetic variation is in part due to people from different backgrounds having children.

Ken said...

Genetic variation that makes a difference to vitamin D levels would by subject to selection Northern Europeans have white skins. If the trait of having lower vitamin d levels is in 20 % of such people (French Canadians) how does this square with selection for maximun fitness. I sounds to me that there are advantages to lower D levels. Vitamin D and aging.).


If you are saying that the D reducing aleles are not native to Europe why have they not been eliminated. An analogy with sickle cell anemia: alleles for this would be eliminated outside the area where they paid off in fitness terms.

"People from different backgrounds having children" - yes a possible explaination but are you really suggesting that 20% of French Canadians a have a non European grandparent.

Cavalli-Sforza - The price of collaboration?

Ken said...

That should be:-
but are you really suggesting that the average French Canadian has a non European grandparent.

Ned Kock said...


I posted recently on vitamin D and aging:

As to your question: grandparent, no, but ancestor, very likely.

There are other evolutionary processes that can account for some of the data you mentioned, such as genetic drift and the evolution of conflicting genes (as in costly traits). I posted about these also:

We would have to look at each individual case, and try to understand it. The cases that you point out are intriguing, and I hope to be able to take a more careful look at them soon.

The two evolutionary processes that I mentioned above are relatively simple versions of more complex population genetics models that Luca Cavalli-Sforza and others studied.

There is also a new field of research known as evolutionary graph theory that leads to even more intriguing results.

viagra online said...

Interesting post and I've been reading a lot about this matters because I am a study of Nutrition and Vitamin D insufficiency can result in thin, brittle, or misshapen bones, while sufficiency prevents rickets in children and osteomalacia in adults, and, together with calcium, helps to protect older adults from osteoporosis.